1. Field of the Invention
The present invention is related to isolated colonocytes enabling early noninvasive detection of colorectal cancer and other gastrointestinal diseases. More particularly, the present invention is related to isolated, biologically substantially pure and viable immunocoprocytes and nonepithelial cells of lymphoid origin obtained from a small fecal sample. The invention is further related to providing a transport medium and a dispersion or suspension medium for isolating viable colonocytes from a fecal sample at normal ambient temperature and a method for detecting colorectal and other gastrointestinal pathology employing the isolated colonocytes of the present invention. The isolated colonocytes also allow the study and determination of other anomalous conditions, symptoms, disorders or pathological conditions.
2. Prior Art
A common gastrointestinal malignancy in humans is colorectal cancer. It has been estimated that colorectal cancer accounts for approximately 14% of all cancer-related deaths in men and women in the United States and its incidence continues to be high (Boring et al, CA Cancer J. Clin. 1994; 44:7-26). Early detection is a critical factor in successful treatment of this cancer, as it is in the treatment of other malignancies.
Screening approaches to detection of colon and colorectal tumors are presently based on the use of (a) fecal occult blood test (FOBT), (b) flexible sigmoidoscopy, (c) double contrast barium enema, and (d) colonoscopy. Among these screening tests only FOBT, which is based on a relatively high probability of bleeding from colorectal tumors, is noninvasive, simple and relatively inexpensive. However, frequent false positive and false negative results of the FOBT considerably limit its specificity and sensitivity. Other procedures are expensive and invasive. Hence, there is a clear need for providing a simple, noninvasive, reliable and inexpensive method for detecting colorectal cancer, gastrointestinal (GI) tract diseases and other pathological conditions.
Colonocytes represent an important source of informational marker molecules that provide a picture of the immediate past metabolic history of the GI tract of a subject. In addition, such cells are representative of the cell population from a statistically large sampling frame reflecting the state of the colonic mucosa along the entire length of the colon in a non-invasive manner, in contrast to a limited sampling by colonic biopsy using an invasive procedure involving endoscopy.
Colonocytes undergo certain changes or transformations and carry certain biological or chemical markers indicative of colonic pathologies including precancerous and cancerous conditions. Therefore, the colonocytes could serve as a valuable early indicator of the onset of neoplastic processes and other pathophysiological changes in the GI tract. Subtle changes in the genes and surface proteins are examples of such neoplastic markers. In particular, Ki67, the cell surface glycoprotein CD44 and tumor-associated antigens 19-9 and lectin binding are specific biomarkers of neoplastic transformation in the GI tract. There is also a strong correlation between the amount of DNA in isolated colonic cells and the presence of tumors, because rapidly dividing cells contain more DNA. It is also well recognized that the development of colonic adenomatous polyps and cancer is a multistep process involving activation of oncogenes (ki-ras), inactivation of tumor-suppressor genes (p53 and APC), and alterations in the DNA mismatch repair genes.
Heretofore, it was generally understood in the art to which this invention belongs that exfoliated colonic cells are destroyed once they are shed into the stools, the reason being that these cells start breaking down as soon as they are exposed to the atmosphere. The enzymes, mucus and the bacteria contained in the stool contribute to the process of destroying the colonic cells. Chilling the freshly collected stool sample to the temperature below −20° C. has been described, for example, in U.S. Pat. Nos. 5,094,956, 5,380,647 and 5,455,160 only for preserving the chemical constituents, without regard to the cellular components. Thus, these procedures do not retain cellular integrity and are not applicable for isolating intact, viable cells free of other impurities.
Dutta and Nair (Gastroenterology, 114:1333-1335, 1998) refer to Albaugh et al (Int. J. Cancer, 52:347-350, 1992) and Iyengar et al (FASEB J. 5: 2856-2859, 1991) for accomplishing isolation of viable colonic cells. Albaugh et al described a transport medium and a procedure to obtain colonocytes from a stool sample based on earlier work of Iyengar et al. However, the transport medium of the prior art was different from the transport medium of the present invention in as much as Albaugh et al's medium consisted of a saline solution to which antibiotics were added in addition to fatty acid free BSA. In other words, the prior art transport medium was deficient at least in one criterion, i.e., in not having a mucolytic agent which is an absolute necessity for the formulation of the transport medium in accordance with the present invention.
Furthermore, in Albaugh et al's system the stool sample after collection had to be kept cooled in ice while being trasported to the laboratory for further processing and could be preserved in ice only for about an hour. In contrast, the system of the present invention does not require cooling in ice and achieves desirable results at the normal ambient temperature which is an important feature of the present invention. Moreover, Albaugh et al state that although their cells had a viability in excess of 80%, the presence of phagocytes and other cells could not be ruled out. Indeed, FIGS. 3 and 4 of Iyengar et al clearly show that the cellular preparations obtained were considerably impure. Thus, the procedures of Iyengar et al and Albaugh et al may provide viable colonocytes, but they are inadequate for the purpose of obtaining substantially pure colonocytes. In summary, heretofore it has not been possible to obtain a viable, biologically subtantially pure sample of a particular cell type isolated at normal ambient atmospheric conditions from a small fecal mass.